Not too many decades ago it seemed "obvious" both to the general public and to sociologists that modern society has changed people’s natural relations, loosened their responsibilities to kin (亲戚) and neighbors, and substituted in their place superficial relati onships with passing acquaintances. However, in recent years a growing body of research has revealed that the "obviousness" is not true. It seems that if you are city resident, you typically know a smaller proportion of your neighbors than you do if you are a resident of a smaller community. But, for the most part, this fact has few significant consequences. It does not necessarily follow that if you know few of your neighbors you will know no one else.
Even in very large cities, people maintain close social ties within small, private social worlds. Indeed, the number and quality of meaningful relationships do not differ between more and less urban people Small-town residents are more involved with kin than are big-city residents. Yet city dwellers compensate by developing friendships with people who share similar interests and activities. Urbanism may produce a different style of life, but the quality of life does not differ between town and city. Nor are residents of large communities any likelier to display psychological symptoms of stress or alienation, a feeling of not belonging, than are residents of smaller communities. However, city dwellers do worry more about crime, and this leads them to a distrust of strangers.
These findings do not imply that urbanism makes little or no difference. If neighbors are strangers to one another, they are less likely to sweep the sidewalk of an elderly couple living next door or keep an eye out for young troublemakers. Moreover, as Wirth suggested, there may be a link between a community’s population size and its social heterogeneity (多样性). For instance, sociologists have found much evidence that the size of a community is associated with bad behavior including gambling, drugs, etc. Large-city urbanites are also more likely than their small-town counterparts to have a cosmopolitan (见多识广者的) outlook, to display less responsibility to traditional kinship roles, to vote for leftist political candidates, and to be tolerant of nontraditional religious groups, unpopular political groups, and so-called un-desirables. Everything considered, heterogeneity and unusual behavior seem to be outcomes of large population size. What is the passage mainly about